The present invention relates to an injection mold for discs such as optical discs, and more particularly to an injection mold for optical discs which has a structure suitable for fixing and exchanging a stamper being mounted on a mold surface of either a movable mold and a stationary mold.
Various structures of a mounting member for mounting the stamper on the mold surface of the mold have been proposed. In general, the stamper is detachably mounted at its peripheral portion and center portion by mounting members.
In the Japanese laid-open utility model publication No. 58-159619, it is disclosed that the stamper is fixed at its peripheral portion by engaging a fixing ring and at its center portion by a stamper fixing pin penetrating the center portion of the stamper, wherein one end of the stamper fixing pin is inserted into a center hole of the mold whilst an opposite end of the stamper fixing pin is provided with a tapered groove so that a wedge-shaped member slidably provided on the mold is engaged with the tapered groove to fix the stamper on the mold.
In the Japanese patent publication No. 62-45809, it is disclosed that the stamper is fixed at its peripheral portion by use of a ring member with screws and at its center portion by a pin-shaped stamper pressing member penetrating the center portion of the stamper, wherein one end of the pin-shaped stamper pressing member is inserted into the mold whilst an opposite end of the pin-shaped stamper pressing member is provided with screws engaged with a gear mechanism externally adjustable to fix and detach the stamper.
The above first conventional structure, where the engagement pin for fixing the center of the stamper provides an advantage of in easy operation but has disadvantages in that the center portion of the stamper is added with offset load whereby the stamper is mounted with a displacement to the mold surface of the mold. This may cause defective mold articles.
The above second conventional structure, where the opposite sides of the engagement pin are fixed with the screws, has disadvantages in complicated operations for detaching the stamper. If, in order to facilitate the external operations, the structure is modified, the modified structure may be complicated resulting in increase in manufacturing cost of the mold.
In order to solve the above problems, the stamper mounting mechanism for mounting the stamper on the mold surface of the mold had been improved for facilitating the fixing and exchanging operations of the stamper and for allowing the quick and sure operations for fixing and exchanging the stamper. The modified stamper mounting mechanism is illustrated in FIGS. 1 and 2. Each of a movable mold 10 and a stationary mold 20 is provided with insert members 12 and 22 in the form of a mold cavity and rings 14 and 24 for positioning the mold cavity. A stamper 30 is provided on the mold surface of the movable mold. Ring members 34 and 36 are mounted in a peripheral portion of the stamper 30. A plurality of claw members 38 are circumferentially and provided at almost constant angle on insides of the ring 14 provided on the movable mold on which the stamper 30 is also mounted. Clearance grooves 40 are provided inside the ring 24 and outside the insert 22 in correspondence to the above claw members 38 so as to allow the claw members 38 to be engaged within the clearance grooves 40 whereby the stamper is detachably mounted at its peripheral portion on the mold surface of the mold.
In the above injection mold, a cyrindrically shaped center pressing member 62 is inserted into and engaged with the center portion of the stamper 30. A plurality of crews 66 are provided on an opposite side of the center pressing member 62 to the side which presses the stamper 30 at circumferentially constant pitch. A cylinder piston 60 forwardly and backwardly operable is placed at the center portion of the movable mold with the mold surface on which the stamper 30 is mounted. An engaging portion is provided at the top of the cylinder piston 60. The engaging portion is made into contact with and engaged with the crews 66 by rotation of the center pressing member. The stamper 30 is detachably mounted on the mold surface of the movable mold by forward and backward movements of the cylinder piston 60.
The cylindrically shaped center pressing member 62 is inserted into and engaged within the center portion of the stamper 30 so as to face to the cylinder piston 60 provided at the center of the movable mold 10. Further, the positioning of the insertion position of the center pressing member 62 to the mold is made by the ring 64 placed at a part of the insert member 12.
In order to fix the center pressing member 62, the crews 66 are provided at circumferentially constant pitch on opposite stamper side (contact portion to the cylinder piston 60 of the center pressing member 62) whilst projections 68 on the top of the cylinder piston 60, which faces to the crews 66, are provided so that the projections 68 are engaged with the crews 66 whereby the center pressing member 62 and the cylinder piston 60 are detachably fixed to each other.
The above third conventional structure has the disadvantages as described below. The ring 64 receives a resin pressure against the center pressing member 62. Since clamp areas formed by the crews 66, the projections 68, and the grooves 70 are positioned inside the ring 64, an inner diameter of the stamper 30 is larger than the diameter of the ring 64. This means it is difficult to reduce the inner diameter of the stamper 30.